Unified constrains for the merge affine mode and the non-merge affine mode

ABSTRACT

Devices, systems and methods for sub-block based prediction are described. In a representative aspect, a method for video processing includes determining a block size constrain, making a determination, based on the block size constrain, about whether or not a merge affine mode and a non-merge affine mode are allowed for a video block in a video frame, and generating a bitstream representation of the video block based on the making the determination.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 17/099,042, filed on Nov. 16, 2020, which is a continuation of International Application No. PCT/IB2019/055244, filed on Jun. 21, 2019, which claims the priority to and benefits of International Patent Application No. PCT/CN2018/092118, filed on Jun. 21, 2018. All the aforementioned patent applications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

This patent document is directed generally to image and video coding technologies.

BACKGROUND

Motion compensation is a technique in video processing to predict a frame in a video, given the previous and/or future frames by accounting for motion of the camera and/or objects in the video. Motion compensation can be used in the encoding and decoding of video data for video compression.

SUMMARY

Devices, systems and methods related to sub-block based prediction for image and video coding are described.

In a representative aspect, the disclosed technology may be used to provide a method for video processing. This method includes determining a block size constrain, making a determination, based on the block size constrain, about whether or not a merge affine mode and a non-merge affine mode are allowed for a video block in a video frame, and generating a bitstream representation of the video block based on the making the determination.

In a representative aspect, the disclosed technology may be used to provide another method for video processing. This method includes determining a block size constrain, making a determination, based on the block size constrain, about whether or not a merge affine mode and a non-merge affine mode are allowed for a video block in a video frame, and generating the video block from a bitstream representation of the video block based on the making the determination.

In yet another representative aspect, the above-described method is embodied in the form of processor-executable code and stored in a computer-readable program medium.

In yet another representative aspect, a device that is configured or operable to perform the above-described method is disclosed. The device may include a processor that is programmed to implement this method.

In yet another representative aspect, a video decoder apparatus may implement a method as described herein.

The above and other aspects and features of the disclosed technology are described in greater detail in the drawings, the description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of sub-block based prediction.

FIG. 2 shows an example of a simplified affine motion model.

FIG. 3 shows an example of an affine motion vector field (MVF) per sub-block.

FIG. 4 shows an example of motion vector prediction (MVP) for the AF_INTER affine motion mode.

FIGS. 5A and 5B show example candidates for the AF_MERGE affine motion mode.

FIG. 6 shows an example of sub-blocks for different components with the 4:2:0 format in JEM.

FIG. 7A shows a flowchart of an example method for video processing.

FIG. 7B shows another flowchart of an example method for video processing.

FIG. 8 is a block diagram illustrating an example of the architecture for a computer system or other control device that can be utilized to implement various portions of the presently disclosed technology.

FIG. 9 shows a block diagram of an example embodiment of a device that can be utilized to implement various portions of the presently disclosed technology.

DETAILED DESCRIPTION

Due to the increasing demand of higher resolution video, video coding methods and techniques are ubiquitous in modern technology. Video codecs typically include an electronic circuit or software that compresses or decompresses digital video, and are continually being improved to provide higher coding efficiency. A video codec converts uncompressed video to a compressed format or vice versa. There are complex relationships between the video quality, the amount of data used to represent the video (determined by the bit rate), the complexity of the encoding and decoding algorithms, sensitivity to data losses and errors, ease of editing, random access, and end-to-end delay (latency). The compressed format usually conforms to a standard video compression specification, e.g., the High Efficiency Video Coding (HEVC) standard (also known as H.265 or MPEG-H Part 2), the Versatile Video Coding standard to be finalized, or other current and/or future video coding standards.

Sub-block based prediction is first introduced into the video coding standard by the High Efficiency Video Coding (HEVC) standard. With sub-block based prediction, a block, such as a Coding Unit (CU) or a Prediction Unit (PU), is divided into several non-overlapped sub-blocks. Different sub-blocks may be assigned different motion information, such as reference index or motion vector (MV), and motion compensation (MC) is performed individually for each sub-block. FIG. 1 shows an example of sub-block based prediction.

Embodiments of the disclosed technology may be applied to existing video coding standards (e.g., HEVC, H.265) and future standards to improve runtime performance. Section headings are used in the present document to improve readability of the description and do not in any way limit the discussion or the embodiments (and/or implementations) to the respective sections only.

1. Examples of the Joint Exploration Model (JEM)

In some embodiments, future video coding technologies are explored using a reference software known as the Joint Exploration Model (JEM). In JEM, sub-block based prediction is adopted in several coding tools, such as affine prediction, alternative temporal motion vector prediction (ATMVP), spatial-temporal motion vector prediction (STMVP), bi-directional optical flow (BIO), Frame-Rate Up Conversion (FRUC), Locally Adaptive Motion Vector Resolution (LAMVR), Overlapped Block Motion Compensation (OBMC), Local Illumination Compensation (LIC), and Decoder-side Motion Vector Refinement (DMVR).

1.1 Examples of Affine Prediction

In HEVC, only a translation motion model is applied for motion compensation prediction (MCP). However, the camera and objects may have many kinds of motion, e.g. zoom in/out, rotation, perspective motions, and/or other irregular motions. JEM, on the other hand, applies a simplified affine transform motion compensation prediction. FIG. 2 shows an example of an affine motion field of a block 200 described by two control point motion vectors V₀ and V₁. The motion vector field (MVF) of the block 200 can be described by the following equation:

$\begin{matrix} \left\{ \begin{matrix} {v_{x} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}x} - {\frac{\left( {v_{1y} - v_{0y}} \right)}{w}y} + v_{0x}}} \\ {v_{y} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{w}x} + {\frac{\left( {v_{1x} - v_{0x}} \right)}{w}y} + v_{0y}}} \end{matrix} \right. & {{Eq}.\mspace{14mu}(1)} \end{matrix}$

As shown in FIG. 2, (v_(0x), v_(0y)) is motion vector of the top-left corner control point, and (v_(1x), v_(1y)) is motion vector of the top-right corner control point. To simplify the motion compensation prediction, sub-block based affine transform prediction can be applied. The sub-block size M×N is derived as follows:

$\begin{matrix} \left\{ \begin{matrix} {M = {{clip}\; 3\left( {4,w,\frac{w \times {MvPre}}{\max\left( {{{abs}\left( {v_{1x} - v_{0x}} \right)},{{abs}\left( {v_{1y} - v_{0y}} \right)}} \right)}} \right)}} \\ {N = {{clip}\; 3\left( {4,h,\frac{h \times {MvPre}}{\max\left( {{{abs}\left( {v_{2x} - v_{0x}} \right)},{{abs}\left( {v_{2y} - v_{0y}} \right)}} \right)}} \right)}} \end{matrix} \right. & {{Eq}.\mspace{14mu}(2)} \end{matrix}$

Here, MvPre is the motion vector fraction accuracy (e.g., 1/16 in JEM). (v_(2x), v_(2y)) is motion vector of the bottom-left control point, calculated according to Eq. (1). M and N can be adjusted downward if necessary to make it a divisor of w and h, respectively.

FIG. 3 shows an example of affine MVF per sub-block for a block 300. To derive motion vector of each M×N sub-block, the motion vector of the center sample of each sub-block can be calculated according to Eq. (1), and rounded to the motion vector fraction accuracy (e.g., 1/16 in JEM). Then the motion compensation interpolation filters can be applied to generate the prediction of each sub-block with derived motion vector. After the MCP, the high accuracy motion vector of each sub-block is rounded and saved as the same accuracy as the normal motion vector.

In the JEM, there are two affine motion modes: AF_INTER mode and AF_MERGE mode. For CUs with both width and height larger than 8, AF_INTER mode can be applied. An affine flag in CU level is signaled in the bitstream to indicate whether AF_INTER mode is used. In the AF_INTER mode, a candidate list with motion vector pair {(v₀, v₁)|v₀={V_(A), V_(B), V_(C)}, v₁={v_(D), v_(E)}} is constructed using the neighboring blocks.

FIG. 4 shows an example of motion vector prediction (MVP) for a block 400 in the AF_INTER mode. As shown in FIG. 4, v₀ is selected from the motion vectors of the sub-block A, B, or C. The motion vectors from the neighboring blocks can be scaled according to the reference list. The motion vectors can also be scaled according to the relationship among the Picture Order Count (POC) of the reference for the neighboring block, the POC of the reference for the current CU, and the POC of the current CU. The approach to select v₁ from the neighboring sub-block D and E is similar. If the number of candidate list is smaller than 2, the list is padded by the motion vector pair composed by duplicating each of the advanced motion vector prediction (AMVP) candidates. When the candidate list is larger than 2, the candidates can be firstly sorted according to the neighboring motion vectors (e.g., based on the similarity of the two motion vectors in a pair candidate). In some implementations, the first two candidates are kept. In some embodiments, a Rate Distortion (RD) cost check is used to determine which motion vector pair candidate is selected as the control point motion vector prediction (CPMVP) of the current CU. An index indicating the position of the CPMVP in the candidate list can be signaled in the bitstream. After the CPMVP of the current affine CU is determined, affine motion estimation is applied and the control point motion vector (CPMV) is found. Then the difference of the CPMV and the CPMVP is signaled in the bitstream.

When a CU is applied in AF_MERGE mode, it gets the first block coded with an affine mode from the valid neighboring reconstructed blocks. FIG. 5A shows an example of the selection order of candidate blocks for a current CU 500. As shown in FIG. 5A, the selection order can be from left (501), above (502), above right (503), left bottom (504) to above left (505) of the current CU 500. FIG. 5B shows another example of candidate blocks for a current CU 500 in the AF_MERGE mode. If the neighboring left bottom block 501 is coded in affine mode, as shown in FIG. 5B, the motion vectors v₂, v₃ and v₄ of the top left corner, above right corner, and left bottom corner of the CU containing the sub-block 501 are derived. The motion vector v₀ of the top left corner on the current CU 500 is calculated based on v₂, v₃ and v₄. The motion vector v₁ of the above right of the current CU can be calculated accordingly.

After the CPMV of the current CU v0 and v1 are computed according to the affine motion model in Eq. (1), the MVF of the current CU can be generated. In order to identify whether the current CU is coded with AF_MERGE mode, an affine flag can be signaled in the bitstream when there is at least one neighboring block is coded in affine mode.

In JEM, the non-merge affine mode can be used only when the width and the height of the current block are both larger than 8; the merge affine mode can be used only when the area (i.e. width×height) of the current block is not smaller than 64.

2. Examples of Existing Methods for Sub-Block Based Implementation

In some existing implementations, the size of sub-blocks (such as 4×4 in JEM) is primarily designed for the luma component. For example, in JEM, the size of sub-blocks is for the 2×2 chroma components with the 4:2:0 format, and for the 2×4 chroma components with the 4:2:2 format. The small size of sub-blocks imposes a higher band-width requirement. FIG. 6 shows an example of sub-blocks of a 16×16 block (8×8 for Cb/Cr) for different components with the 4:2:0 format in JEM.

In other existing implementations, in some sub-block based tools such as the affine prediction in JEM, MVs of each sub-block are calculated with the affine model as shown in Eq. (1) independently for each component, which may result in misalignment of motion vectors between luma and chroma components.

In yet other existing implementations, in some sub-block based tools such as affine prediction, the usage constrains are different for the merge mode and the non-merge inter mode (a.k.a. AMVP mode, or normal inter-mode), which need to be unified.

3. Exemplary Methods for Sub-Block Based Prediction in Video Coding

Sub-block based prediction methods include unifying the constraints for the merge affine mode and the non-merge affine mode. The use of sub-block based prediction to improve video coding efficiency and enhance both existing and future video coding standards is elucidated in the following examples described for various implementations.

Example 1. The merge affine mode and the non-merge affine mode are allowed or disallowed with the same block size constraint.

-   -   (a) The block size constrain depends on the width and height         compared to one or two thresholds. For example, both the Merge         affine mode and the non-merge affine mode are allowed if the         width and the height of the current block are both larger than M         (e.g., M equal to 8), or width is larger than M0 and height is         larger than M1 (e.g., M0 equal to 8 and M1 equal to 4);         otherwise, both the Merge affine mode and the non-merge affine         mode are not allowed. In another example, both the Merge affine         mode and the non-merge affine mode are allowed if the width and         the height of the current block are both larger than M (e.g., M         equal to 16); otherwise, both the Merge affine mode and the         non-merge affine mode are not allowed.     -   (b) The block size constrain depends on the total number of         samples within one block (i.e., the area width×height). In one         example, both the Merge affine mode and the non-merge affine         mode are allowed if the area (i.e. width×height) of the current         block is not smaller than N (e.g., N equal to 64); Otherwise,         both the Merge affine mode and the non-merge affine mode are not         allowed.     -   (c) For the merge affine mode, it can be an explicit mode with         signaling a flag as in JEM, or it can be an implicit mode         without signaling a flag as in other implementations. In the         latter case, the affine merge candidate is not put into the         unified merge candidate list if the merge affine mode is not         allowed.     -   (d) For the non-merge affine mode, when affine is disallowed         according to above rules, the signaling of indications of affine         mode is skipped.

The examples described above may be incorporated in the context of the methods described below, e.g., methods 700 and 750, which may be implemented at a video encoder and video decoder, respectively.

FIG. 7A shows a flowchart of an exemplary method for video processing. The method 700 includes, at operation 710, determining a block size constrain of a video block in a video frame. At operation 720, making a determination, based on the block size constrain, about whether or not a merge affine mode and a non-merge affine mode are allowed for the video block. At operation 730, generating a bitstream representation of the video block based on the making the determination.

In some embodiments, the generating the bitstream representation includes coding the video block using the merge affine mode by including an indication of the merge affine mode in the bitstream representation. In some embodiments, the generating the bitstream representation includes coding the video block using the non-merge affine mode by including an indication of the non-merge affine mode in the bitstream representation. In some embodiments, the generating the bitstream representation includes coding the video block using the merge affine mode by omitting an indication of the merge affine mode in the bitstream representation, thereby implicitly indicating the merge affine mode. In some embodiments, the generating the bitstream representation includes coding the video block using the non-merge affine mode by omitting an indication of the non-merge affine mode in the bitstream representation, thereby implicitly indicating the non-merge affine mode.

In some embodiments, the generating the bitstream representation includes generating the bitstream representation from the video block such that the bitstream omits an explicit indication of the merge affine mode due to the determination that the block size constrain disallowed the merge affine mode. In some embodiments, the generating the bitstream representation includes generating the bitstream representation from the video block such that the bitstream omits an explicit indication of the non-merge affine mode due to the determination that the block size constrain disallowed the non-merge affine mode. In some embodiments, the block size constrain of the video block includes a height of the video block and a width of the video block that are each greater than a common threshold. In some embodiments, the common threshold is eight, and the merge affine mode and the non-merge affine mode are allowed in response to the height of the video block and the width of the video block being greater than the common threshold. In some embodiments, the common threshold is sixteen, and the merge affine mode and the non-merge affine mode are allowed in response to the height of the video block and the width of the video block being greater than the common threshold.

In some embodiments, the block size constrain of the video block includes a height of the video block greater than a first threshold and a width of the video block greater than a second threshold, and the first threshold and the second threshold are different. In some embodiments, the block size constrain of the video block includes a height of the video block and a width of the video block, and a product of the height and the width is greater than a threshold.

FIG. 7B shows another flowchart of an exemplary method for motion compensation. The method 750 includes, at operation 760, determining a block size constrain of a video block in a video frame. At operation 770, making a determination, based on the block size constrain, about whether or not a merge affine mode and a non-merge affine mode are allowed for the video block. At operation 780, generating the video block from a bitstream representation of the video block based on the making the determination.

In some embodiments, the bitstream representation includes an indication of the merge affine mode, and the video block is generated using the merge affine mode by parsing the bitstream representation according to the indication. In some embodiments, the bitstream representation includes an indication of the non-merge affine mode, and the video block is generated using the non-merge affine mode by parsing the bitstream representation according to the indication. In some embodiments, the bitstream representation omits an indication of the merge affine mode, and wherein the video block is generated using the merge affine mode by parsing the bitstream representation in absence of the indication of the merge affine mode. In some embodiments, the bitstream representation omits an indication of the non-merge affine mode, and the video block is generated using the non-merge affine mode by parsing the bitstream representation in absence of the indication of the non-merge affine mode.

In some embodiments, the block size constrain of the video block includes a height of the video block and a width of the video block that are each greater than a common threshold. In some embodiments, the block size constrain of the video block includes a height of the video block greater than a first threshold and a width of the video block greater than a second threshold, and the first threshold and the second threshold are different. In some embodiments, the block size constrain of the video block includes a height of the video block and a width of the video block, and a product of the height and the width is greater than a threshold.

The methods 700 and 750, described respectively in the context of FIGS. 7A and 7B, may further include processing the block of video data based on a motion compensation algorithm. In some embodiments, the motion compensation algorithm may be affine motion compensation prediction, alternative temporal motion vector prediction (ATMVP), spatial-temporal motion vector prediction (STMVP), pattern matched motion vector derivation (PMMVD), bi-directional optical flow (BIO) or decoder-side motion vector refinement (DMVR).

In a representative aspect, the above-described methods 700 and/or 750 are embodied in the form of processor-executable code and stored in a computer-readable program medium. In yet another representative aspect, a device that is configured or operable to perform the above-described methods are disclosed. The device may include a processor that is programmed to implement the above described methods 700 and/or 750. In yet another representative aspect, a video encoder apparatus may implement method 700. In yet another representative aspect, a video decoder apparatus may implement method 750.

4. Example Implementations of the Disclosed Technology

FIG. 8 is a block diagram illustrating an example of the architecture for a computer system or other control device that can be utilized to implement various portions of the presently disclosed technology, including (but not limited to) methods 700 and/or 750. In FIG. 8, the computer system 800 includes one or more processors 805 and memory 810 connected via an interconnect 825. The interconnect 825 may represent any one or more separate physical buses, point to point connections, or both, connected by appropriate bridges, adapters, or controllers. The interconnect 825, therefore, may include, for example, a system bus, a Peripheral Component Interconnect (PCI) bus, a HyperTransport or industry standard architecture (ISA) bus, a small computer system interface (SCSI) bus, a universal serial bus (USB), IIC (I2C) bus, or an Institute of Electrical and Electronics Engineers (IEEE) standard 674 bus, sometimes referred to as “Firewire.”

The processor(s) 805 may include central processing units (CPUs) to control the overall operation of, for example, the host computer. In certain embodiments, the processor(s) 805 accomplish this by executing software or firmware stored in memory 810. The processor(s) 805 may be, or may include, one or more programmable general-purpose or special-purpose microprocessors, digital signal processors (DSPs), programmable controllers, application specific integrated circuits (ASICs), programmable logic devices (PLDs), or the like, or a combination of such devices.

The memory 810 can be or include the main memory of the computer system. The memory 810 represents any suitable form of random access memory (RAM), read-only memory (ROM), flash memory, or the like, or a combination of such devices. In use, the memory 810 may contain, among other things, a set of machine instructions which, when executed by processor 805, causes the processor 805 to perform operations to implement embodiments of the presently disclosed technology.

Also connected to the processor(s) 805 through the interconnect 825 is a (optional) network adapter 815. The network adapter 815 provides the computer system 800 with the ability to communicate with remote devices, such as the storage clients, and/or other storage servers, and may be, for example, an Ethernet adapter or Fiber Channel adapter.

FIG. 9 shows a block diagram of an example embodiment of a mobile device 900 that can be utilized to implement various portions of the presently disclosed technology, including (but not limited to) methods 700 and/or 750. The mobile device 900 can be a laptop, a smartphone, a tablet, a camcorder, or other types of devices that are capable of processing videos. The mobile device 900 includes a processor or controller 901 to process data, and memory 902 in communication with the processor 901 to store and/or buffer data. For example, the processor 901 can include a central processing unit (CPU) or a microcontroller unit (MCU). In some implementations, the processor 901 can include a field-programmable gate-array (FPGA). In some implementations, the mobile device 900 includes or is in communication with a graphics processing unit (GPU), video processing unit (VPU) and/or wireless communications unit for various visual and/or communications data processing functions of the smartphone device. For example, the memory 902 can include and store processor-executable code, which when executed by the processor 901, configures the mobile device 900 to perform various operations, e.g., such as receiving information, commands, and/or data, processing information and data, and transmitting or providing processed information/data to another device, such as an actuator or external display.

To support various functions of the mobile device 900, the memory 902 can store information and data, such as instructions, software, values, images, and other data processed or referenced by the processor 901. For example, various types of Random Access Memory (RAM) devices, Read Only Memory (ROM) devices, Flash Memory devices, and other suitable storage media can be used to implement storage functions of the memory 902. In some implementations, the mobile device 900 includes an input/output (I/O) unit 903 to interface the processor 901 and/or memory 902 to other modules, units or devices. For example, the I/O unit 903 can interface the processor 901 and memory 902 with to utilize various types of wireless interfaces compatible with typical data communication standards, e.g., such as between the one or more computers in the cloud and the user device. In some implementations, the mobile device 900 can interface with other devices using a wired connection via the I/O unit 903. The mobile device 900 can also interface with other external interfaces, such as data storage, and/or visual or audio display devices 904, to retrieve and transfer data and information that can be processed by the processor, stored in the memory, or exhibited on an output unit of a display device 904 or an external device. For example, the display device 904 can display a video frame that includes a block (a CU, PU or TU) that applies the intra-block copy based on whether the block is encoded using a motion compensation algorithm, and in accordance with the disclosed technology.

In some embodiments, a video encoder apparatus or decoder apparatus may implement a method of sub-block based prediction as described herein is used for video encoding or decoding. The various features of the method may be similar to the above-described methods 700 or 750.

In some embodiments, the video encoding and/or decoding methods may be implemented using a decoding apparatus that is implemented on a hardware platform as described with respect to FIG. 8 and FIG. 9.

From the foregoing, it will be appreciated that specific embodiments of the presently disclosed technology have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the presently disclosed technology is not limited except as by the appended claims.

Implementations of the subject matter and the functional operations described in this patent document can be implemented in various systems, digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Implementations of the subject matter described in this specification can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a tangible and non-transitory computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more of them. The term “data processing unit” or “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.

A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Computer readable media suitable for storing computer program instructions and data include all forms of nonvolatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

It is intended that the specification, together with the drawings, be considered exemplary only, where exemplary means an example. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Additionally, the use of “or” is intended to include “and/or”, unless the context clearly indicates otherwise.

While this patent document contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all embodiments.

Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document. 

1. A method of processing video data, comprising: determining, for a conversion between a current video block of a video and a bitstream of the video, that whether or not a first affine mode and a second affine mode are allowed for the current video block based on a same dimension constrain; and performing, based on the determining, the conversion between the current video block and the bitstream, wherein the first affine mode and the second affine mode are not allowed in response to either a height of the current video block or a width of the current video block being smaller than or equal to 8, and the bitstream omits an indication for the first and second affine mode, wherein determining that whether or not a first affine mode and a second affine mode are allowed for the current video block based on a same dimension constrain comprises: determining that the bitstream omits an indication of the first affine mode at least based on a dimension of the current video block; and determining that the bitstream omits an indication of the second affine mode at least based on a dimension of the current video block, wherein the first affine mode and the second affine mode are not allowed in response to either a height of the current video block or a width of the current video block being smaller than or equal to
 8. 2. The method of claim 1, wherein in the first affine mode, motion information of control points of the current video block is derived at least based on an affine candidate of the current video block and without applying motion vector differences (MVD).
 3. The method of claim 2, wherein the first affine mode is a merge affine mode, and the second affine mode is a non-merge affine mode.
 4. The method of claim 2, wherein the first affine mode is a direct affine mode, and the second affine mode is a non-direct affine mode.
 5. The method of claim 1, wherein the first affine mode and the second affine mode are not allowed in response to a height and a width of the current video block being both smaller than or equal to a threshold.
 6. The method of claim 1, wherein the conversion includes encoding the current video block into the bitstream.
 7. The method of claim 1, wherein the conversion includes decoding the current video block from the bitstream.
 8. An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to: make a determination, for a conversion between a current video block of a video and a bitstream-of the video, that whether or not a first affine mode and a second affine mode are allowed for the current video block based on a same dimension constrain; and perform, based on the determination, the conversion between the current video block and the bitstream, wherein the instructions cause the processor to: determine that the bitstream omits an indication of the first affine mode at least based on a dimension of the current video block; and determine that the bitstream omits an indication of the second affine mode at least based on a dimension of the current video block, wherein the first affine mode and the second affine mode are not allowed in response to either a height of the current video block or a width of the current video block being smaller than or equal to
 8. 9. The apparatus of claim 8, wherein in the first affine mode, motion information of control points of the current video block is derived at least based on an affine candidate of the current video block and without applying motion vector differences (MVD).
 10. The apparatus of claim 9, wherein the first affine mode is a merge affine mode, and the second affine mode is a non-merge affine mode.
 11. The apparatus of claim 9, wherein the first affine mode is a direct affine mode, and the second affine mode is a non-direct affine mode.
 12. The apparatus of claim 8, wherein the first affine mode and the second affine mode are not allowed in response to a height and a width of the current video block being both smaller than or equal to a threshold.
 13. A non-transitory computer-readable storage medium storing instructions that cause a processor to: determine, for a conversion between a current video block of a video and a bitstream-of the video, that whether or not a first affine mode and a second affine mode are allowed for the current video block based on a same dimension constrain; and perform, based on the determining, the conversion between the current video block and the bitstream, wherein the instructions cause the processor to determine that the bitstream omits an indication of the first affine mode at least based on a dimension of the current video block; and determine that the bitstream omits an indication of the second affine mode at least based on a dimension of the current video block, wherein the first affine mode and the second affine mode are not allowed in response to either a height of the current video block or a width of the current video block being smaller than or equal to
 8. 14. The non-transitory computer-readable storage medium of claim 13, wherein in the first affine mode, motion information of control points of the current video block is derived at least based on an affine candidate of the current video block and without applying motion vector differences (MVD).
 15. The non-transitory computer-readable storage medium of claim 14, wherein the first affine mode is a merge affine mode, and the second affine mode is a non-merge affine mode.
 16. The non-transitory computer-readable storage medium of claim 14, wherein the first affine mode is a direct affine mode, and the second affine mode is a non-direct affine mode.
 17. A non-transitory computer-readable recording medium storing a bitstream which is generated by a method performed by a video processing apparatus, wherein the method comprises: determining, for a conversion between a current video block of a video and a bitstream-of the video, that whether or not a first affine mode and a second affine mode are allowed for the current video block based on a same dimension constrain; and generating the bitstream based on the determining, wherein determining that whether or not a first affine mode and a second affine mode are allowed for the current video block based on a same dimension constrain comprises determining that the bitstream omits an indication of the first affine mode at least based on a dimension of the current video block; and determining that the bitstream omits an indication of the second affine mode at least based on a dimension of the current video block, wherein the first affine mode and the second affine mode are not allowed in response to either a height of the current video block or a width of the current video block being smaller than or equal to
 8. 18. The non-transitory computer-readable storage medium of claim 17, wherein in the first affine mode, motion information of control points of the current video block is derived at least based on an affine candidate of the current video block and without applying motion vector differences (MVD).
 19. The non-transitory computer-readable storage medium of claim 18, wherein the first affine mode is a merge affine mode, and the second affine mode is a non-merge affine mode.
 20. The non-transitory computer-readable storage medium of claim 18, wherein the first affine mode is a direct affine mode, and the second affine mode is a non-direct affine mode. 